Inhibition of Excised Tomato Roots by Sulfanilamide and Its Reversal by P-Aminobenzoic Acid and N-Pteroylglutamic Acid.

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Abstract
Sulfanilamide inhibited growth of excised tomato roots grown in sterile culture; stimulation was observed at low concns. Both p-aminobenzoic acid (PABA) and N-pteroylglutamic acid overcame the inhibition. Competitive antagonism was indicated in both cases. Methionine was slightly antagonistic. Various purines and pyrimidines were ineffective either in the presence or absence of methionine. Inhibition by excess PGA was relieved by an inhibitory concn. of sulfanilamide. In the absence of sulfanilamide both PABA and PGA stimulated growth of main axis and laterals. Stimulation of growth of main axis was not necessarily accompanied by the same effect on laterals, and vice versa. PABA and PGA were inhibitory at lower concns. than usually found with microorganisms.